The present invention relates to an optical detector which is generally used in optical communication, and to an optical information apparatus, optical measurement, an analysis apparatus and the like.
Heretofore, the devices which have been most generally used as light-to-current converters are photomultipliers, charged coupled devices ("CCDs"), and photodiodes.
With respect to photomultipliers, an advantage thereof is that the photomultiplier responds to very weak light and hence the amplification factor thereof is large, while a disadvantage thereof is that the response speed is low, i.e., on the order of microseconds, the conversion current is small, i.e., on the order of microamperes, and the correlation between light intensity and current density varies to some degree whereby both the dark current and the noise levels are large.
In addition, the CCD does not directly convert light into current, but temporarily converts light into electric charge and then converts the electric charge into current in the stage of reading the electric charge. For this reason, the CCD has an advantage in that the correlation between light intensity and current is extremely high, while it has a disadvantage in that the response speed is low due to the two stages of the conversion process. In addition, the conversion mechanism of the CCD is complicated.
Further, with respect to the photodiode, it is an advantage that the bandwidth is wide, i.e., 20 GHz, while it is a disadvantage that the range of operation temperatures is narrow, i.e., in the range of 10 to 40.degree. C.
It is an object of the present invention to provide an optical pumping field emission type light-to-current converter which utilizes field emission so that the amount of field emission current is increased to realize a response speed on the order of picoseconds (10.sup.-12 seconds) and having a structure that is simplified.